High voltage transfer switch with cam controlled overlap during transfer

Abstract

A transfer switch to selectively transfer an electrical load from one high voltage source to another includes a shaft connected to a handle. Spaced close to opposite ends of the shaft are two circular slotted cams. Cam followers connected to opposite ends of a follower bar are inserted in the cam slot. The follower bars connected to the cam followers are connected to vacuum interrupter contacts (mechanical vacuum relays). The transfer switch is constructed so that as the cam is rotated the contacts connecting one high voltage source to the electrical load are closed and as the cam is continued to be rotated the contactors of the previously connected high voltage supply are subsequently released.

What is claimed is: 
     
       1. A transfer switch to selectively couple output terminal means to accept a load to first and second input terminal means to accept a first and second high voltage power source respectively comprising first electric contact means to interconnect said first input terminal means to said output terminal means, second electrical contact means to interconnect said second input terminal means to said output terminal means, means to operate said first and second electrical contact means including cam wheel means, rotatable shaft means to support said cam wheel means, said cam wheel means including first and second cam slots, first and second cam follower means engaged with said first and second cam slots, respectively, constraining means to constrain said first and second cam follower means to have linear motion, said first and second cam follower means connected to impart the motion of said first and second cam follower means to operate said first and second electrical contact means, said first and second cam slots having coordinated profiles so that said first and second follower bars are linearly displaced in sequence whereby one of said first and second electrical switches is engaged before the other of said electrical switches is subsequently disengaged. 
     
     
       2. A transfer switch as defined in claim 1 wherein said cam wheel means comprises first and second cam wheels mounted close to opposite ends of said rotatable shaft means and each of said cam wheels having the first and second cam slots, said first cam follower means comprising a first follower bar of nonconductive material and including roller followers at each end which are inserted into the first cam slot of said first and second cam wheels, and said second cam follower means comprises a second follower bar of nonconductive material and includes roller followers at each end which are inserted into the second cam slot of said first and second cam wheels. 
     
     
       3. A transfer switch as defined in claim 2 wherein said constraining means comprises a first pair of guide ways connected to opposite ends of said first follower bar and a second pair of guide ways connected to opposite ends of said second follower bar. 
     
     
       4. A transfer switch as defined in claim 3 wherein said first electrical contact means comprises a first and second vacuum interrupter contact type switch connected to respond to a linear displacement of said first follower bar and said second electrical contact means comprises a third and fourth vacuum interrupter contact type switch connected to respond to a linear displacement of said second follower bar. 
     
     
       5. A transfer switch arrangement to selectively couple first and second input terminal means to accept a high voltage source to output terminal means to accept a load to be energized comprising, cam means including at least a cam wheel having first and second cam slots therein, a rotatable shaft to support said cam wheel, follower means including first and second follower bars having first and second cam followers engaged with said first and second cam slots, respectively, follower bar constraint means to constrain said follower bars to linear motion, and first and second electrical contact means responsive to a linear displacement of said first and second follower bars to interconnect said first and second input terminal means to said output terminal means, said first cam slot having a first cam profile whereby a first rotation of said shaft causes said first electrical contact to open, said second cam slot having a second cam profile complementary to said first cam profile whereby said first rotation of said shaft causes said second electrical contact to close before said first electrical contact opens, and a rotation of said shaft opposite said first rotation causes said second electrical contact to open and said first electrical contact to close before said second electrical contact opens. 
     
     
       6. A transfer switch as defined in claim 5 wherein said first cam slot profile encompasses an arc of at least from 0° to 120° wherein the radial extent of said first cam slot profile is uniform for an arc of 0° to 75° and decreases in magnitude for an arc from 75° to 120° and said second cam slot profile encompasses an arc of at least from 300° to 180° wherein the radial extent of said second cam slot profile is uniform for an arc of 300° to 225° and decreases in magnitude for an arc of 225° to 180°. 
     
     
       7. A transfer switch to selectively couple first and second input means to accept a high voltage source to output means to accept a load comprising cam wheel means including, first and second cam slots in opposite halves of the cam wheel means, rotatable shaft means to support said cam wheel means, first and second cam follower means mechanically coupled to said first and second cam slots, respectively, guide means to limit said first and second cam followers to linear motion and first and second electrical contact means responsive to a linear displacement of said first and second cam follower means, said first and second electrical contact means electrically coupling said first and second input means to said output means, respectively, said first cam slot having a first cam surface profile to linearly displace said first cam follower for a defined arc of rotation of said cam wheel means, said second cam slot having a second cam surface profile to linearly displace said second cam follower for a defined arc of rotation of said cam wheel means, said first and second cam profiles coordinated to affect said linear displacements of said first and second cam follower means in sequence.